mirror of
https://github.com/jackyzha0/quartz.git
synced 2025-12-27 23:04:05 -06:00
141 lines
4.0 KiB
Markdown
141 lines
4.0 KiB
Markdown
---
|
|
title: "13-databases-1"
|
|
aliases:
|
|
tags:
|
|
- cosc203
|
|
- lecture
|
|
sr-due: 2022-12-02
|
|
sr-interval: 41
|
|
sr-ease: 250
|
|
---
|
|
|
|
# What is a database
|
|
- an integrated collection of data
|
|
- implicit properties
|
|
- represents some aspect of th real world, called miniworld
|
|
- is a coherent collection of data with inherent meaning
|
|
- is designed built and populated with data for a specific purpose
|
|
|
|
## DBMS
|
|
- a software system designed to store, manage, and facilitate access to the database
|
|
- Oracle, SQL erver, MySQL, MonogDB
|
|
|
|
## Application program
|
|
- a program that provides access to the dtabase by sending queries and requests for data to the DBMS
|
|
|
|
|
|
|
|
# This course
|
|
- modelling and design of DBs
|
|
- programming (SQL + appliation development)
|
|
- DBMS implementation
|
|
|
|
specifiically *relational databases*
|
|
- ER modelling
|
|
- datbase normalisation
|
|
- SQL
|
|
|
|
## relational vs nosql
|
|
relation is better for structured data, nosql is better for abstract data, as it is more flexible
|
|
|
|
# Data modelling
|
|
first step in designing database
|
|
- create a data model for a specific problem domain
|
|
|
|
a model is Defn: a collection of concepts that can be used to describe the structure of a database such as data types, relationsips, and contraints that should hold for the data
|
|
|
|
schema Defn: a collection of metadata that describes the logical view of a database
|
|
|
|
noSQL databases are either schema-free or have relaxed schemas
|
|
|
|
|
|
|
|
## conceptual data modelling
|
|
model the data close to the way the users percieve the data
|
|
|
|
ER model
|
|
- popular high level conceptual model
|
|
- uses diagrammatic notations - er diagram (ERD)
|
|
|
|
three notations
|
|
- chens notation
|
|
- crows foot notation
|
|
- UML notation
|
|
|
|
# Example
|
|
|
|
|
|
|
|
|
|
# how to model
|
|
## entities
|
|
- a thing in the real world with independent existence
|
|
- physical existence
|
|
- conceptial existence
|
|
|
|
entity type is a collection of entities with the same attributes — represented by a rectangle
|
|
|
|
|
|
|
|
## attribute
|
|
- a property of an entity
|
|
- simple (atomic) e.g, first name
|
|
- composite (can be divided) e.g., address
|
|
- single value e.g., id number
|
|
- multi value e.g., siblings
|
|
- stored - by default
|
|
- derived - drawn as dashed ovals e.g., age is derived from birth date
|
|
- key
|
|
- unique
|
|
- simple or composite
|
|
- underlined in ERD
|
|
|
|
|
|
|
|
## relationships
|
|
a relationship model the connection between entitiy types
|
|
|
|
e.g., each employee works for one department
|
|
|
|
relationship type is a set of relationsihps among entities from the particular entity types
|
|
- represented by diamonds
|
|
|
|
|
|
|
|
|
|
relationship types can have attributes
|
|
|
|
properties
|
|
- degree
|
|
- binary [binary relationship|200](https://i.imgur.com/QDpdMo7.png)
|
|
- n-ary [n-ary relationship|300](https://i.imgur.com/7oIJP5j.png)
|
|
- cardinality for binary relationships
|
|
- one to one
|
|
- one to n
|
|
- m to n
|
|
- participation
|
|
- total participation
|
|
- marked by double line
|
|
- relationship is required
|
|
- partial
|
|
- marked by single line
|
|
- relationsihp is not required
|
|
|
|
|
|
|
|
|
|
## weak entities
|
|
- regular types have key attributes
|
|
|
|
- weak types do not have their own key attributes
|
|
- they are identified by their relationship with another entity
|
|
- this creates and identifying relationship
|
|
- must have a total participation constraint
|
|
- the other entity type is called the identifying or owner entity type
|
|
- denoted by double lined rectable and double lined diamond
|
|
- have a partial key
|
|
- a set of attributes that uniquiely identify the weak entities that are related to the same owner entity
|
|
|
|
|
|
|